A transparent coating with long-term performance could help wood maintain its share of residential markets against material substitution and potentially expand markets in recreational property and non-residential buildings. While transparent coatings can be made reasonably resistant to UV some UV likely penetrates to the wood and by necessity clear coatings are transparent to visible light. Visible light can also cause damage over the long term thus the underlying wood needs additional protection. Four novel UV protection systems were tested as pre-treatments on uncoated wood and under three coatings, a water-based film forming coating, a water-based acrylic varnish and a solvent based water repellent. Samples were exposed to natural weathering facing South at 45° at a test site in Gulfport, Mississippi, in collaboration with the USDA Forest Products Laboratory. The test material was inspected every six months for discolouration, mold and stain, coating water repellency, flaking, erosion and cracking and substrate condition. After 24 months exposure, coatings over the combination of UV absorber and lignin stabilizer identified by Stephen Ayer were performing better than the same coatings applied over the combination recommended by Ciba and coatings over both pre-treatments were performing substantially better than controls with no pre-treatment. Projection of fitted curves beyond the data appears to indicate that pretreatment may double the life expectancy of the coating. There was no consistent effect of the synergists on either combination at this time.
In southwestern B.C., CCA-treated wood is being increasingly used for balcony support posts. However, these are not required to meet CSA standards. After only 4.5 years in service there were signs of decay in 105 mm square CCA-treated posts removed from one Vancouver condominium complex. Three of these posts with particularly low preservative retention and penetration were severely decayed. Four more were slightly damaged by decay. Overall, the posts would not have met the penetration and retention requirements in CSA standards and were put into a critical application in a high hazard environment in contact with untreated wood. The size and the preservative retention suggest that this was material treated for the Japanese market that failed to meet the penetration or grading requirements of the JAS standard and was therefore sold locally. There is a wealth of evidence to show that material meeting CSA standards can meet or exceed service life expectations. However, confidence in the performance of treated wood can easily be damaged by the poor performance of substandard material. Unfortunately, there is currently no requirement for treated wood used in buildings to have third-party assurance of standards conformance.
The major defining characteristic of lumber cut from trees that have been infected with the mountain pine beetle is the extent of fungal bluestain in the sapwood. Forintek Canada Corp. scientists have previously observed that bluestained wood appears to have different dimensional stability characteristics than non-stained wood when subjected to repeated wetting and drying. Bluestained wood has also been reported to show increased permeability, which may make treatment with liquids such as wood preservatives easier. However, no data is available on how bluestained wood resulting from the beetle attack might affect. We therefore identified the need to generate data on the dimensional stability, checking, and permeability characteristics of bluestained wood compared with non-stained wood.
To examine dimensional stability, specimens of bluestained and non-stained 2 x 4 in. lumber were subjected to wetting/drying cycles. After 5 and 10 cycles, the amount of bow, crook, cupping, twist, and checking was measured. The permeability of the wood was also determined by weighing end-matched specimens before and after a 1-, 4-, and 24-hour dip or after a pressure treatment cycle with chromated copper arsenate preservative, and then calculating the uptake and preservative retention.
The results clearly show that when repeatedly wetted and dried, such as occurs in exterior end uses, bluestained beetle-killed wood is more dimensionally stable (less cupping and twist) and checks less than non-stained sapwood, but is more permeable to water. The stresses appear to be relieved by many micro-checks rather than fewer large checks. Overall, the improved dimensional stability should result in the lumber made from stained wood remaining straighter.
Increased permeability of the bluestained wood was confirmed by data showing enhanced chromated copper arsenate (CCA) uptake and penetration. One implication of the stained sapwood treating more readily than non-stained wood is that in batches of preservative-treated wood, the stained wood is liable to be overtreated or the non-stained wood undertreated. As anticipated, bluestain in the sapwood had no effect on the penetration of preservative into the heartwood, the most refractory part of the wood. Treatment with CCA also masked the bluestain by coloring it green.
The increased permeability probably also has implications for ease of air or kiln drying and possibly reduced degrade in the kiln.
Insects - Attack on trees
Stains - Fungal
Pinus contorta Dougl. var. latifolia - Defects
Preservatives - Permeability
Preservatives - Penetration
Pinus contorta Dougl. var. latifolia - Preservation
This report evaluates a new fluctuating pressure treating process, with a small pressure variation, that could be easily implemented into a treating plant with a control value. Coastal western hemlock being a relatively difficult species to impregnate was chosen as a suitable test species. Incised and unincised hemlock was used to relate to present industry practices.
The recently revived interest in borate treatment for the production of termite-resistant lumber has led to the need for more rapid treatment processes. Pre-steaming prior to pressure treatment was known to have a number of potential benefits in terms of improved permeability, moisture distribution and vacuum. This process was therefore tried on western hemlock and amabilis fir Dodai (baby squares) in an attempt to achieve through-treatment without a diffusion period after pressure treatment. Western hemlock pre-steamed to a core temperature of 65 degrees C received a 25% increase in solution uptake and a 41% increase in mean heartwood penetration using a two hour pressure period. Amabilis fir pre-steamed to a core temperature of 90 degrees C received a 40% increase in solution uptake but no measurable increase in heartwood penetration. This was because penetration measured from the heartwood face was virtually complete in the amabilis fir treated without pre-steaming. Pre-steaming hemlock and amabilis fir Dodai appears to be a very effective means of improving uptake during pressure treatment. Further optimisation of this process is still possible.
The recent interest in borate treatment for the production of termite-resistant lumber has led to the need for improved treatment processes. Pre-steaming prior to pressure treatment was known to have a number of potential benefits in terms of improved permeability, moisture distribution and effectiveness of the vacuum. This process was therefore tried on western hemlock dodai (105 mm squares) in an attempt to achieve 80% cross sectional penetration with a minimal diffusion period after pressure treatment. Western hemlock pre-steamed to a core temperature of 82 degrees C in four hours took up almost double the amount of treating solution of end-matched unsteamed samples. There was an improvement in mean heartwood penetration of 45% immediately after treatment and a 134% increase in penetration after one week storage. This was not entirely due to diffusion within the wood but to mass flow of treating solution continuing after the end of the pressure process. After one week storage 64% of samples had 80% of the cross section penetrated. Reducing the vacuum time from 30 minutes to zero had a detrimental effect on penetration. Increasing time under vacuum to 60 minutes provided no beneficial effect. Pre-steaming of hemlock dodai appears to be a very effective means of improving uptake during pressure treatment.
Commercialisation of a low-maintenance transparent coating is expected to assist wood products to maintain residential market share in the face of competing materials and potentially expand market share in recreational and non-residential applications. Testing of a range of commerical products had identified one outstanding performer and arrangements were made to work with the developer of this coating to further improve its performance, targeting a 15-year life under Canadian conditions. A series of exposure tests were set up to evaluate potential improvements in resistance to UV and to black stain fungi. This report covers the initiation of a test of the second generation of UV protectant pre-treatments and biocide combinations. It also evaluated the apparent beneficial effect of a supposedly inert formulating agent. UV protectant combinations were tested under a water-based two-step transparent coating and under a water-based clear exterior urethane. The biocide combinations were used as pre-treatments and incorporated in steps one and two of the water-based two-step transparent coating. After six months' exposure in Mississippi and Vancouver, all the material in the UV protectant test was rated 7 or higher on a 0 to 10 scale. There were early indications of deterioration for the controls with Inert B (no UV protectants), for 2.5% HALS and for 7.5% HALS. Most of the downgrading was due to black stain fungi, suggesting that the biocide combination and concentration used in this part of the test was still inadequate to provide long-term protection. In the biocides test there was a substantial beneficial effect on black stain resistance of additional coats of step one. It was clearly beneficial to have some pre-treatment and it was also clearly important to include the biocides in the coating and not just in the pre-treatment. There were early indications of a positive effect from the incorporation of ZnO with the organic biocides. There was no consistent pattern to allow the effects of Inerts A and B to be distinguished.
Forintek is Canada's primary source of test data on preservatives and treated wood, consequently it is imperative that Forintek maintain test sites representative of Canadian climates, particularly the worst case, southwestern B.C. Forintek's western field test site at Westham Island closed down in 1997 and work has been underway to establish a new site at the Malcolm Knapp Research Forest. This report documents the site evaluation, environmental status, site plan and location, soil preparation and trail relocation, soil characterization, a sediment runoff problem, sign shelter construction, fence treatment and installation and relocation of shingle and shake test racks. The test site was ready to receive above ground test material in the summer of 2002. Installation of ground-contact tests can proceed in summer of 2003.
Commercialisation of a low maintenance transparent coating is expected to assist wood products to maintain residential market share in the face of competing materials and potentially expand markets in recreational property and non-residential applications. Four areas for improvement were identified: optimizing the UV blocking capability of the coating, improving black stain resistance of the coating, improving UV resistance of the underlying wood and improving black stain resistance of the underlying wood. This study focussed on improving UV/visible light resistance of the underlying wood and the effect of the UV protectants on resistance to black stain. Samples of ponderosa pine sapwood were pre-treated with a range of individual compounds with potential as UV protectants and a range of combinations of these compounds. Half of each sample was finished with two coats of the first step and one coat of the second step of a two-step water based transparent coating. The other half was finished with three coats of transparent water based urethane. The first set of samples was exposed for 2000 hours in an Atlas Weather-Ometer®. The weathering cycle was full time UV and full time misting using diffusers over the spray nozzles, except the mist was turned off for one hour each workday. The samples were evaluated using a set of criteria developed by the USDA Forest Products Laboratory at Madison. Comparable samples were pre-treated with the same series of UV protectant systems then one half was finished with two coats of the first step and one coat of the second step of a two-step water based transparent coating. The other half was left unfinished. Four combinations of biocides were added to this part of the experiment. The second set of samples was inoculated with a spore suspension of black stain fungi and exposed for 2000 hours in damp chambers at 20° C. These samples were evaluated for stain intensity on a 0 to 5 scale.
Uncoated samples exposed in the Weather-Ometer showed severe weathering leaving the wood completely white with loose surface cells. Controls with no pre-treatment showed virtually the same level of damage under the water based urethane though the coating itself remained largely in place albeit with considerable cracking. The only individual UV protectant that showed substantial protection against UV under the water based transparent urethane was a UV absorber (UVA), Tinuvin 1130. The two-step transparent water based coating proved so effective at stopping UV that there was no damage to the underlying wood, even for the control with no pre-treatment. It did suffer from discolouration with whitening and blackening in places, types of colour change not seen under normal service conditions. The suggested the constant UV and water may have created conditions conducive to chemical reactions not seen in service such as conversion of transparent iron oxides from iron III to iron II.
None of the other UV protectants combined with the UVA provided any substantial improvement to its performance. Several of the UV protectants had adverse effects on performance. The colloidal zinc oxide caused blistering of the water based transparent urethane. The trans iron oxides turned black possibly due to reduction from iron III to iron II. Lignostab caused a yellow discolouration of the water-based transparent urethane in reference samples not exposed to light.
Several of the UV protectants appeared to increase the growth of mold and stain fungi on the samples. All four biocide combinations were very effective at controlling mold and stain fungi. The results of these tests were used to design a field test of UVA and biocide combinations.
The lumber industry producing hem-fir, a mixture of western hemlock and amabilis fir, is interested in marketing a termite-resistant wood product in regions where subterranean termites adversely affect consumer confidence in wood-frame construction. The use of borate treatment appears to be a promising approach to overcoming the difficulty of pressure treating unincised hem-fir. This experiment was designed to scientifically confirm whether increasing solution temperatures could increase the penetration of borates into western hemlock, which is the less treatable species of the hem-fir mix. This study was designed to quantify the effect of increasing borate solution temperatures from ambient (approx. 20°C), currently used in commercial treating plants, to 35°C and 50°C on kiln-dried and green western hemlock. Increasing the solution temperature increased the initial uptake in kiln-dried lumber, but the difference was minimal with green lumber. Conversely, the effect of increasing the solution temperature on continued penetration during storage was greater for the green material than the kiln-dried. The kiln-dried samples did not show much movement after two weeks storage, whereas the green material had good diffusion over two weeks, meeting the AWPA standard at 50°C, and would likely continue beyond the two weeks. These results suggest a commercial treating plant will gain optimum penetration of borates using higher solution temperatures on green lumber with a one to two-week diffusion period. Penetration of borate into kiln-dried lumber was also shown to improve greatly using heated solutions, although only the 50°C/4-hour treatment/2-week storage met the AWPA standard in this study.